The invention relates generally to particulate filtration. In particular, the invention relates specifically to mesoporous filtration using ceramic metal oxides based on particular grain sizes.
Contaminants in drinking water present high risks to human health; pathogenic microorganisms, disinfectant by-products, arsenic and heavy metals can cause cancer and other toxic effects. Organic and inorganic agents such as pesticides, ammonium perchlorate (Al(ClO4)3), arsenic (As), nitrite (NO2−), sulfate (SO42−), radon (Rn), particulates and pathogens including cyst-like organisms and emerging pathogens like caliciviruses, microsploridia, hepatitis A virus and Legionella must be removed from drinking water.
Filtration and separation can be accomplished with porous membranes. A microfiltration membrane process presents a cost-effective medium for rapid removal of chemical and biological agents from water. However, microfiltration does not provide efficient removal of nanometer-sized bacteria, viruses and metal ions. Ultrafiltration (UF) membranes with nominal pore diameters (measured in angstroms) of 20 Å to 200 Å are used in a variety of solid-liquid separation processes, representing a fairly large market in the sectors of waste remediation, drink clarification, oil processing and fractionation of biomolecules.
Polymer membranes supplies much of the market for ultrafiltration membranes. These are limited in their application by chemical and thermal stability, mechanical strength and pore size distribution. See R. W. Baker et al., Membrane Separation Systems, Noyes Data Corporation, Parkridge, N.J. (1991), and R. R. Bhave, Inorganic Membranes, Van Nostrand, Reinhold, N.Y. (1991). In contrast, commercial ceramic membranes, such as Membralox® and Carbosep®, have significantly better thermal, chemical and mechanical stability than organic membranes. However, these ceramic membranes are limited by tortuous, irregularly sized pores that lead to fouling, poor separations and inefficient permeance. See Canadian Patent 1,168,590 to Arod et al. have used ceramic ultrafiltation membranes (pore size 20 nm to 40 nm) to remove contaminants from used motor oil.
Contaminant removal has been demonstrated at far lower energy consumption than distillation and with a far smaller waste stream than with the conventional acid treatment followed by centrifugation. See A. Deschamps et al., “Application of Inorganic Membranes in Refining Processes of Petroleum Residues”, Proc. 1st Intn'l. Conf. Inorganic Membranes, 237 (July 1990), regarding ceramic ultrafiltation membranes (pore diameter above 15 nm) to separate catalyst particles from a hydrocarbon stream at 250° C.
Ceramic ultrafiltation membranes have also been shown to be effective in separation of oil from aqueous streams, as reported in Bhave, Inorganic Membranes. About 99.5% of lubricating oil in a 0.1% oil/balance water stream was rejected by ceramic membranes. A water flux of 7.5 L/h-m2 across the membrane (4 nm to 50 nm pore size) was obtained with a trans-membrane pressure of 3 bar, as reported by R. R. Bhave et al., “Removal of Oily Contaminants in Wastewater with Microporous Alumina Membranes,” AlChE Symp. Ser., 84, 261, p. 19 (1988).